Recent machine tools, such as for example those manufactured by Machining Center or NC, have progressed to the state where very high speeds of operation are utilized in which a blade sometimes rotates over 30,000 r.p.m. In such machine tools, if the blade and its holder are not balanced or are even slightly unbalanced, deflection increases during high speed machining, which adversely affects machining accuracy. In the past, the balance of the tool holder was commonly adjusted by drilling a hole on the higher side of the mass. In this way, although unbalancing of the tool holder itself could be eliminated, such attempts were unsuccessful in adjusting unbalance caused by attaching a blade like collet, drill, end-mill, tap or the like to the tool holder.
In order to solve the above problem, a tap-process is applied with a certain pitch from the outer circle of the flange provided on the main body of the tool holder toward the center of the holder and then, hollow sets are inserted at unbalanced points. However, difficulties were encountered in adjusting all of the unbalance. Therefore, such attempts were inadequate in adjusting a balance grade smaller than 2.5G, which is required in connection with tool holders rotatable over 30,000 r.p.m., a trend of the latest machine tools.
Thus, there has been a need for a balanceable tool holder for machine tools, which would eliminate the problems and limitations associated with the prior devices discussed above, most significant of the problems being the need to balance the tool holder even when blade like collets, drills, end-mills, taps or the like are used in connection with the tooling holder at high speed r.p.m. These and other objects will be apparent from the following detailed description and appended claims.